1. Field of the Invention
The present invention relates to a processing method and a processing apparatus for carving a workpiece using a rotary tool. More specifically, it relates to a processing method and a processing apparatus for carving a concave or a convex portion having a predetermined configuration to, for instance, a mold material using an end mill.
2. Description of Related Art
Conventionally, a workpiece is carved using a rotary tool such as an end mill as follows. First, as shown in FIG. 10, the rotary tool T enters a processing surface of the workpiece W at a right angle to carve to a predetermined cutting depth. Subsequently, the rotary tool T is moved parallel to the processing surface of the workpiece W to cut at a constant depth while keeping the predetermined cutting depth to carve a concave portion and a convex portion.
However, according to the above cutting method, an entire blade of the pointed end of the rotary tool T touches the workpiece W when the rotary tool T enters the processing surface of the workpiece W at a right angle. Consequently, a load applied to the rotary tool T increases abruptly when the rotary tool T touches the workpiece W, thereby decreasing the tool""s life span.
A method for solving the above disadvantage has been proposed. As shown in FIG. 11, the rotary tool T first approaches the processing surface of the workpiece W while revolving (helical movement) a central axis of the rotary tool T, and the rotary tool T enters the processing surface of the workpiece W to a predetermined depth. Subsequently, the rotary tool T is moved parallel to the processing surface of the workpiece W to cut the workpiece W keeping the cutting depth to carve the concave portion and the convex portion.
According to the cutting method shown in FIG. 11, the load applied to the rotary tool T in cutting (starting to contact) the workpiece W can be reduced as compared to the method shown in FIG. 10.
However, subsequently to the cutting, the rotary tool T is moved parallel to the processing surface of the workpiece W while keeping the predetermined cutting depth and the workpiece W is carved successively by touching an entire side of the rotary tool T to the workpiece W. Accordingly, the load applied to the rotary tool T abruptly increases in initiating the actual carving step and decrease the tool""s life span is decreased.
The above-described load increase in starting the actual cutting can not be solved by the cutting method shown in FIG. 11.
Further, the rotary tool T has to be moved in helical movement to enter the processing surface of the workpiece W when a groove is carved by the cutting method shown in FIG. 11. Accordingly, the diameter of the rotary tool T has to be at least smaller than the groove to be carved, which means that the diameter of the rotary tool T has to be small in accordance with a width of the groove. Therefore, the tool is likely to be broken or damaged because of insufficient strength.
An object of the present invention is to provide a processing method and a processing machine for restraining an abrupt increase of a load applied to a tool in cutting and for avoiding a decrease in the tool""s life span to cope with the above-described problem.
A processing method according to the present invention is for carving a workpiece using a rotary tool. The processing method is characterized in having the steps of entering the rotary tool obliquely to the processing surface of the workpiece by relatively moving the rotary tool and the workpiece; and carving the workpiece by relatively moving the rotary tool and the workpiece in a direction opposite to the moving direction during the entering step.
Obliquely entering the rotary tool to the processing surface of the workpiece refers to moving the rotary tool along the processing surface of the workpiece while gradually increasing a cutting depth of the rotary tool.
An entering angle of the rotary tool in obliquely entering the processing surface of the workpiece is preferably moderate relatively to the processing surface and is preferably determined in relation to a cutting depth.
In relatively moving the rotary tool in the direction opposite to the moving direction, the rotary tool is not necessary to move on the same locus as the entering locus, but the locus may be slightly diverged relatively to the entering direction.
The rotary tool and the workpiece may be relatively moved one-dimensionally or two-dimensionally. However, the rotary tool and the workpiece are preferably arranged to be movable in three-dimensional directions (X, Y and Z-axis directions orthogonal with each other. An end mill and a milling cutter are preferably used for the rotary tool.
According to the above arrangement, since the rotary tool and the workpiece are relatively moved so that the rotary tool enters obliquely to the processing surface of the workpiece, a load applied to the rotary tool in entering gradually increases. In other words, the load applied to the rotary tool does not increase abruptly, thereby restraining a decrease in tool""s life span.
Subsequently, the rotary tool and the workpiece are moved relative to each other in a direction opposite to the X and Y moving direction during the entering step while keeping the depth constant. A sloping portion left by the rotary tool in entering obliquely to the processing surface of the workpiece in the previous step is gradually carved when the rotary tool moves in the direction opposite to the entering direction. Accordingly, the load applied to the rotary tool is not abruptly increased, thereby also restraining the decrease in tool""s life span.
In the above arrangement, the rotary tool and the workpiece may be relatively moved while keeping a constant cutting depth of the workpiece by the rotary tool during the carving step.
Alternatively, the rotary tool and the workpiece may be relatively moved while gradually increasing the cutting depth of the workpiece by the rotary tool during the carving step. According to the above arrangement, initial section of the carving step constitutes second entering step. Accordingly, since the cutting depth per one cut can be determined by the first oblique entering (entering step) and subsequent cutting in the opposite direction (second entering step), the increase of the load applied to the tool can be further moderate. The carving step may be subsequently performed while keeping a constant cutting depth.
A processing machine according to the present invention includes a table for the workpiece to be set onto; a rotary tool; a spindle head to which the rotary tool is attached; a machine body having the table and the spindle head relatively movable in three-dimensional directions; and a controller for controlling a drive of the machine body. The processing machine is characterized in that the controller includes a means for relatively moving the rotary tool and the workpiece so that the rotary tool obliquely enters the processing surface of the workpiece and the rotary tool subsequently moves in a direction opposite to the entering direction.
According to the above arrangement, the effect of the above-described processing method, i.e. restraining the abrupt increase of the load applied to the rotary tool in entering the workpiece to avoid the decrease in tool""s life span can be obtained. Further, since the relative movement of the rotary tool and the workpiece is done automatically, the processing can be efficiently conducted.